1. Field of the Invention
The present invention relates to a reproduction device, a reproduction method and a computer usable medium having a computer readable reproduction program embodied therein for decoding compressed musical data and reproducing the decoded musical data while suppressing the occurrence of a gap causing sound interruption between pieces of music.
2. Description of the Related Art
Various musical data compression technologies such as MP3 (MPEG-1 Audio Layer III) and AAC (Advanced Audio Coding) have been standardized due to the spread of portable digital audio players (DAP).
In such compression technologies, data of a piece of music is managed as one music source, and one music source is divided into frames and compressed (encoded). In an encoding process of obtaining compressed musical data from a music source, a modified discrete cosine transform (MDCT) is used. An MDCT transform is performed making adjacent frames overlap each other, thereby having the advantage of preventing the occurrence of a noise on the boundary between the adjacent frames.
On the other hand, since an MDCT transform makes adjacent frames overlap each other, it needs, when expanding (decoding) data of a frame, data of a frame just before the frame to be expanded. Therefore, in encoding using an MDCT transform, a leading frame to which a silent portion is added is produced before the leading position of musical data. Likewise, an end frame to which a silent portion is added is produced after the end position of the musical data.
FIG. 1 shows an example of a waveform of the leading portion of a music source before encoding, and an example of a waveform of the leading portion of compressed musical data after encoding. As shown in FIG. 1, the compressed musical data after encoding is divided into frames, and a silent portion is added to the leading portion. The compressed musical data after encoding in FIG. 1 causes a delay of sound emission as compared with the musical data before encoding due to addition of a silent portion to the leading portion. FIG. 2 shows an example of a waveform of the end portion of a music source before encoding, and an example of a waveform of the end portion of compressed musical data after encoding. As shown in FIG. 2, a silent portion is added also to the end portion of the compressed musical data after encoding.
By the way, music compact discs (CDs) include so-called live disks on which a live performance music constituted by pieces of music connected with each other is recorded. When encoding is performed every music source of a piece of music obtained by playing back a live disk by a compression technology using the MDCT transform described above to produce compressed musical data, and then the compressed musical data is decoded to be reproduced, a gap occurs between the end portion of a piece of music and the leading portion of the next piece of music. By the occurrence of this gap, the sound is interrupted momentarily and an unnatural sound is reproduced.
The following techniques of eliminating such a gap between pieces of music are known.
(1) When music is switched from a piece of music to the next piece of music, cross-fade that fades out the sound of the end portion of a reproduced piece of music and simultaneously fades in the sound of the leading portion of a piece of music reproduced next (the next reproduced piece of music) is performed for several seconds, thus reproducing the pieces of music in such a manner, a gap between the pieces of music is inconspicuous. FIG. 3 shows an example of a waveform in which a reproduced piece of music indicated with a broken line and the next reproduced piece of music indicated with a solid line are cross faded.
(2) Information about the length of a music source is stored when encoding the music source, and gaps between pieces of music are eliminated based on the information, thereby reproducing the pieces of music without the occurrence of gaps between the pieces of music.
(3) Music sources of a plurality of pieces of music having no silent portion between pieces of music such as music sources of a live disk are stored in one file, thereby reproducing the pieces of music without the occurrence of gaps between the pieces of music. This technique is disclosed in Japanese Patent Application Laid-Open No. 2004-93729.
However, in the case of technique (1), pieces of music are not connected continuously as shown in FIG. 3, so that reproduced sound is unnatural. In the case of technique (2), a player reproducing pieces of music while eliminating gaps between pieces of music is limited to one corresponding to a device (encoder) which performs the encoding. In other words, the player is required to previously know what kind of encoding was performed. In the case of technique (3), the player is limited to one corresponding to the encoder as in the case of technique (2). Furthermore, the whole of music sources of two or more pieces of music is stored in one file, so that it is difficult to reproduce a desired piece of music immediately.